1. Field of the Invention
The invention relates to a phase locked loop (PLL), and more particularly to a PLL for attenuating harmonics.
2. Description of the Related Art
Phase locked loops (PLL) are commonly used in circuits that generate a high-frequency signal with a frequency being an accurate multiple of the frequency of a reference signal. PLLs can also be found in applications where the phase of the output signal has to track the phase of the reference signal, hence the name phase-locked loop. For example, a PLL can be used in a frequency synthesizer of a radio receiver or transmitter for generating a local oscillator signal, which is a multiple of a stable, low-noise and often temperature-compensated reference signal. As another example, a PLL can also be used for clock recovery applications in digital communication systems, disk-drive read-channels, etc.